1. Technical Field of the Invention
The present invention relates to an IC (Integrated Circuit) testing apparatus. More particularly, it relates to an IC testing apparatus which eliminates the phase shift between the signals applied to a device to be tested.
2. Description of the Related Art
When IC's such as RAM's (Random Access Memory) are manufactured, it is necessary to test whether or not the manufactured IC's are working properly and possess the desired function. Generally, an IC testing apparatus is employed in the testing process.
A simple example of the operation of an IC testing apparatus will be explained for the case where the device to be tested (hereinafter, referred to as test device) is a RAM. First, an IC testing apparatus is connected to a RAM by means of a plurality of address lines, a plurality of data lines, and a clock signal line such as for Row Address Strobe (RAS) signals. When the connection is completed, data is written in a memory location designated by the address lines via the data lines. Afterwards, the written data is read. Then this read data is compared to the written data and is determined whether the two pieces of data are identical or not. The testing process is thus performed by repeating the process of comparing the read data with the written data for each designated memory location.
As mentioned above, because the IC testing apparatus and the test device are connected by means of a plurality of address lines and a plurality of data lines, a phase difference is generated between the signals transmitted through each of the lines. This phase difference is referred to as skew.
This skew generally represents the phase or temporal shift from the expected value of the amplitude generated between signals, when identical signals are transmitted through a plurality of transmission lines. In the case of IC testing apparatuses, the problem originates in the dispersion of the driving characteristics of the driver and such, which drives the signals to be applied to the test devices.
When the above described phase difference is generated, adjustments are made by varying the amount of delay by inserting a delay line in between the connection lines, or by substituting an oscilloscope or such for the delay line and varying the amount of delay using the oscilloscope or such.
Generally, however, the above described testing process is not performed by connecting one IC testing apparatus with one test device. Instead, one IC testing apparatus is connected to a plurality of test devices, so a large amount of test devices are being tested simultaneously. Therefore, there is a need for phase adjustments of the signals applied to the test devices for each individual test devices. In addition, since there is a large number of lines used in connecting to each individual test devices, there are problems in eliminating the phase differences among each of the signals, such as requiring of a great amount time and being extremely laborious.